1. Technical Invention
The present invention relates to a small-sized electric motor which includes a connecting portion of a stator winding with less occupying space and equalized electric resistance in every phase, thereby facilitating a connection work and not producing non-uniformity in torque.
2. Background Art
A DC brushless motor has been increasingly applied to electronic equipment in recent years because of its simple construction and superior maintainability, being easy to construct in small size, and being easily driven by three phase AC power source controlled by power electronics, and the like. In combination with the recent progress in various apparatus and equipment of smaller size and lower price, the demand for the DC brushless motor is still increasing.
As one of the apparatus which copes with such demand, for example, the Japanese Patent Publication (unexamined) No. 18345/1999 discloses a stator for a electric motor (hereinafter referred to as DC brushless motor) in which stator windings are wound around a coil bobbin mounted on a stator core of the DC brushless motor, and each stator winding of same phase of the stator windings is connected through conductors. This known stator of the DC brushless motor comprises: an engaging groove provided on a flange of the mentioned coil bobbin for holding a starting end or a terminal end of the mentioned stator winding; a connection board formed into a disc of an insulating material, having a plurality of circular grooves on one end in radial direction, and provided with an insertion hole communicating to the mentioned groove on the other end; and a conductive member for each phase provided with a terminal segment having a U-shaped groove on the side of a belt-like conductor, the belt-like conductor being inserted in the groove of the mentioned connection board, and the terminal segment being projected from the mentioned insertion hole. As a result of such construction, it is reported that the connection between the stator winding of each phase and the conductive member for each phase is simplified, and the yield of materials is improved.
In such construction, a common conductive member of each phase is formed into a belt-shape with the same cross-sectional area as the conductive member for each phase and inserted in the groove of the mentioned connection board. The terminal segment thereof projects from the mentioned insertion hole in the same manner as the terminal segment of the conductive member for each phase. The terminal segment of the conductive member for each phase projects in the direction of external diameter of the mentioned connection board. On the other hand, the terminal segment of the common conductive member projects in the direction of internal diameter the mentioned connection board, and is connected to the stator winding of each phase.
In the stator of conventional DC brushless motor, however, as to the projecting direction of the terminal segment connected to the starting end or terminal end of the stator winding, a following point is to be noted. That is, the terminal segment of the conductive member for each phase projects in the direction of external diameter of the connection board, while the terminal segment of the common conductive member projects in the direction of internal diameter of the connection board. Therefore, a problem exists in that a space occupied by the connecting portion between each terminal segment and the starting end or terminal end of the stator winding is large over both internal and external diameter directions of the connection board. In particular, the connecting portion with the terminal segment of the common conductive member projecting in the internal diameter direction constitutes barrier that may be an obstacle in an attempt to shorten the DC brushless motor in axial direction. Another problem exists in that, at the time of connecting the terminal segment of the common conductive member to the starting end or terminal end of the stator winding, insertion of the tools for connection is not easy making it difficult to perform the connection work.
Moreover, the conductive members for each phase are formed of a material of the same cross-sectional area despite that they are formed with different diameters respectively. Therefore, a further problem exists in that there arises an irregularity in electric resistance value for each phase due to difference in length of the conductive members, etc., whereby non-uniformity in magnetic fluxes takes place in magnetic poles of each phase due to irregularity in current, eventually resulting occurrence of non-uniformity in torque.
Note that this type of DC brushless motor is usually used with a current in the range of approximately 50 to 100A under source voltage of 12 V, and impedance of each phase is originally small. Consequently, for example, in the case of using the DC brushless motor as a steering drive for vehicles, such occurrence of delicate non-uniformity in torque influenced by the irregularity of electric resistances of the conductive members for each phase undesirably gives a driver a feeling something like difficulty in adapting himself or herself to the manipulation and a sense of unease. As a result, a DC brushless motor without non-uniformity in torque has been heretofore desired for long.
The present invention was made to solve the above-discussed problems and has an object of providing a small-sized and inexpensive electric motor that facilitates connection of stator coil, capable of being constructed in small size, and provided with a connecting portion of the stator coil in which electric resistance is equalized and stable torque characteristic is obtained.
A electric motor according to the invention comprises:
a plurality of stator coils wound around a magnetic pole of a stator core, and of which lead wires are led to an external diameter side in the vicinity of one end of the stator core;
a connecting conductor holder being an insulating annular member having a through hole at the central part, in which a plurality of accommodating grooves opened to one side and formed in belt shape in circumferential direction are provided in diameter direction so as to be located in close proximity to the lead wires of the stator coils;
first and second connecting conductors having a belt-like conductor accommodated in said accommodating grooves of said connecting conductor holder, and connecting terminals provided projecting from the mentioned belt-like conductor to the external diameter side of said connecting conductor holder and each connected to a predetermined lead wire of said stator coils;
wherein the lead wires of the stator coils of same phase are connected to each other through the first connecting conductor, and the lead wires to be connected to an electrically neutral point of the stator coils are connected through the second connecting conductor.
As a result of such construction, it is possible to insert and operate the connecting tools easily, and to perform connection work easily, thereby achieving a connecting portion of high reliability.
It is also preferable that the connecting conductor holder has the through hole for forming a space in which a bearing-housing portion is inserted, the bearing-housing portion supporting a bearing of the electric motor arranged in the vicinity of the connecting conductor holder.
As a result, it is possible to insert and arrange the bearing-housing portion in the through hole, thereby reducing its length in axial direction, eventually resulting in a small sized electric motor. Furthermore, it is also possible to insert and arrange a coupling with other equipment driven in the electric motor in the like manner, making it possible to small size the whole apparatus including the driven equipment.
It is also preferable that the first connecting conductor has a sectional area to make electric resistance of each phase equal after connecting the lead wires of the stator coils.
As a result, no strong or weak magnetic flux due to uneven current arises, and it is possible to prevent occurrence of non-uniformity in torque.
It is also preferable that the first connecting conductor has an external terminal formed by bending an end part of the belt-like conductor toward a side where the connecting terminal is provided.
As a result, it is possible to achieve a first connecting conductor of good yield and inexpensive.
It is also preferable that the second connecting conductor serves as a connecting conductor plate comprising a conductor plate mounted on a side of the connecting conductor holder located on the opposite side of projecting connecting terminals of the first connecting conductor, and connecting terminals projecting from the conductor plate to the external diameter side of the connecting conductor holder.
As a result, distance between one connecting terminal and another of the first and the second connecting conductors becomes larger, and it is possible to perform the connection work more easily, thus achieving a connecting portion of high reliability.
It is also preferable that the connecting conductor plate is composed of conductor plate segments and a plurality of connecting conductor plates having connecting terminals provided projecting from the conductor plate segment.
As a result, it is possible to achieve a second connecting conductor of good yield and inexpensive.